Nocardiosis is a pyogranulomatous suppurative infection of skin and/or lungs that may show widespread dissemination. It is caused by Nocardia spp., an aerobic gram-positive partially acid-fast bacterium which is a common soil saprophyte. Infection occurs after wound contamination, inhalation, and ingestion, particularly in immunocompromised animals. This is a rare serious condition. Prognosis is guarded, and the disease tends to be chronic, extensive and refractory. A six-year-old male mongrel cat was presented with a history of chronic ulceration for over two years, which appeared six months after the treatment of an abscess at the groin. The cat was then submitted to various therapies, which showed no improvement. At the time of clinical presentation, the patient was receiving sulfamethoxazole and trimethoprim at incorrect dosage and frequency. It was noted an ulcerative lesion with irregular configuration and mild purulent exudate, at the left inguinal area. Suspected diagnosis included opportunistic mycobacterial infections, nocardiosis, and actinomycosis. Cytological examination of the exudate failed to demonstrate an infectious agent. The biochemical profile was normal. The complete blood cell count showed leucocytosis with neutrophilia, monocytosis and eosinophilia. A skin biopsy was performed and the fragments were submitted to bacterial culture and histopathological examination, which were inconclusive. Systemic enrofloxacin and topical Burrow's solution for 20 days showed no response, and the lesion progressed; there were many fistulae with remarked purulent exudate around the initial lesion. A surgical drainage was performed and a second biopsy was taken; fragments were again submitted to bacterial culture and histopathological examination. Biopsy findings revealed a diffuse dermatitis with multiple clusters of filamentous branched acid-fast bacteria. Culture isolation demonstrated Nocardia spp. The cat was initially treated with systemic clarithromycin combined with amoxycillin for two months, showing an improvement of about 70%. Biweekly subcutaneous applications of cefovecin were added to the therapy and demonstrated to hasten the clinical resolution. Data from veterinary textbooks report that nocardiosis is mainly caused by N. asteroids or N. brasiliensis. The species could not be determined in this case, and molecular techniques will be applied in order to identify it. Insufficient duration of therapy may lead to disease recurrence. At the time of abstract submission, the cat had still been successfully treated with clarithromycin, amoxycillin, and cefovecin for five months.